An image forming device by an electrophotographic system performs repeated image formation by successively executing respective steps of charging, exposure, development, transfer, and cleaning by a charger, an exposing unit, a developing unit, a transfer unit, a cleaning unit, and the like which are disposed in the vicinity on the outer peripheral surface of a photoreceptor for forming an electrostatic latent image, thereby outputting a printed image. Recently, there is also present a cleaning-less system for simultaneously carrying out a cleaning step in a developing step.
A development method of an electrophotographic system includes dry development using a powdered toner and liquid development using a developing solution having a toner dispersed in a liquid. Of these, the dry development includes a one-component development system using only a toner as a developer and a two-component development system using a toner and a carrier (magnetic particle). In addition, the one-component development system is classified into a magnetic one-component development system and a non-magnetic one-component development system depending upon the presence or absence of magnetism of the toner.
In the respective development systems, it is generally carried out by using a developing roller in a columnar form as a developer carrier which comes into contact with or becomes adjacent to a photoreceptor to feed a developer.
For example, since in order to carry a carrier or a magnetic toner, it is required to dispose a magnet roller internally, a cylindrical base body having a space therein is used as a developing roller to be used in the two-component development system or magnetic one-component development system. Furthermore, since a developing roller to be used in the non-magnetic one-component development system is not required to be cylindrical, in the contact system, there may be the case where a soft organic urethane rubber roller or the like is used, while in both the contact system and the non-contact system, a cylindrical base body having a space therein is used, also for the reason of weight reduction or the like.
In general, a metal is used as the quality of material for the cylindrical base body, and in the two-component development system or the magnetic one-component system, for the sake of not obstructing a magnetic force by the internally disposed magnet roller, an aluminum alloy which is anon-magnetic body is frequently used. Besides the aluminum alloy, for example, Patent Document 1 describes a magnet roller for magnetic brush development using a non-magnetic austenitic stainless steel tube. Furthermore, Patent Document 2 describes a developer carrier (developing roller) using an aluminum alloy and also suggests the use of an iron alloy. In addition, Patent Document 3 describes a support for developing roller containing from 1 to 3% by weight of manganese. Moreover, Patent Document 4 describes a developer carrier (developing roller) using an austenitic stainless steel welded tube (electro-resistance-welded tube).
In the non-magnetic one-component development system, an aluminum alloy having excellent processability is also frequently used. Besides the aluminum alloy, for example, Patent Document 5 describes that an iron based metal, STKM, a ferritic stainless steel alloy, or SUS430 is used as a developing roller to be used in the one-component contact development system. This is aimed to provide a uniform a butting pressure by using a magnetic body as a developing roller and using an elastic body magnet roller as a toner resisting roller.
Furthermore, the outer peripheral surface of a cylindrical metal base body is subjected to a variety of treatments or provided with a rubber or resin layer as the need arises. In addition, in an end section of a cylindrical metal base body, for the purpose of holding the base body and rotationally driving it, it is generally configured to provide a small diameter central shaft body coaxial with the cylindrical metal base body. As a method for providing such a central shaft body in the end section of the cylindrical base body, there is known a method for press fitting a metal flange having a central shaft body in the end section of the cylindrical base body.
As described previously, the non-magnetic one-component development system includes a non-magnetic one-component contact development system in which a photoreceptor and a developing roller come into contact with each other and a non-magnetic one-component non-contact development system in which a photoreceptor and a developing roller become adjacent to each other in a non-contact state. An electrophotographic developing roller to be used in such a non-magnetic one-component non-contact development system has a non-contact development function such that a toner to be fed from a toner container via feed rollers is formed into a prescribed thin layer on a developing roller, delivered in the vicinity of the surface of a photoreceptor drum and applied onto an electrostatic latent image on the surface of the foregoing photoreceptor drum having a gap with the developing roller by an alternating current bias voltage to be applied to the developing roller, thereby achieving development. In such a non-contact development system, since the surface of the developing roller can be made of a hard metal material, there is an advantage that the life is long as compared with soft organic urethane rubber rollers to be used in the case of contact development. Also, since the foregoing developing roller for non-magnetic one-component does not require a magnet within the developing roller, there is obtained an advantage that it is inexpensive as compared with developing rollers having a magnet roller for magnetic toner. However, with respect to the matters that the non-magnetic toner be formed into a uniform thin layer on the developing roller and that the toner be uniformly charged with a stably necessary and sufficient charge amount to obtain a surface state of the developing roller suitable for delivery in the vicinity of the surface of the photoreceptor drum, a degree of difficulty is high.
On the other hand, recently, in the electrophotographic device, response to full coloration is developing, too. Following this, in the full-color electrophotographic device, a non-magnetic developer of a one-component development system has become frequently used. The one-component development system is a system in which a developer is adhered with a frictional electrification amount of the developer without using a carrier and delivered, thereby achieving development. In the non-magnetic one-component development system, there are merits that the maintenance is easy because a carrier is not used; that it is possible to make the unit small in size because a magnet is not required within a developer carrier; and that it is inexpensive.
In the non-magnetic one-component non-contact development system, the developer is held on the surface of the developing roller due to an image force and delivered in the vicinity of the surface of the photoreceptor due to rotation of the developing roller, thereby achieving development. Since this image force depends upon a frictional electrification amount of the developer as generated due to friction of the developer with the surface and a layer thickness restricting member of the developing roller, surface roughness (formation of irregularities) of the developing roller is extremely important. For that reason, for the developing roller, ones resulting from coating a resin on a cylindrical metal base body and ones resulting from subjecting a cylindrical metal base body to a treatment such as mechanical processing and plating are used, and aluminum alloys are broadly used as the cylindrical metal base body. For example, Patent Document 4 describes a blast treated developer carrier; Patent Document 6 describes a developer supporting member (developing roller) resulting from a blast treatment and subsequently a hard plating treatment; and Patent Document 2 describes a developer carrier (developing roller) using an aluminum alloy or an iron alloy resulting from a blast treatment, an etching treatment or an electroless plating, respectively.
For a photoreceptor drum and a developing roller to be mounted in an electrophotographic device of a full-color non-magnetic one-component non-contact development system, in order to respond to registration accuracy of primary color images necessary for full coloration, it is required to make a gap between the photoreceptor drum and the developing roller highly uniform. In recent full-color electrophotographic devices, it is necessary to have an extremely high shape accuracy such that an outside diameter deflection characteristic in the photoreceptor drum and the developing roller is not more than 30 μm, and further not more than 20 μm in the state that a shaft is provided. This is because in the case where the outside diameter deflection is large at the time of rotational driving of the developing roller, since in delivering the developer from the developing roller to the photoreceptor drum, a surface distance between the developing roller and the photoreceptor drum becomes non-uniform, the delivery amount of the developer to the photoreceptor drum having a latent image thereon becomes non-uniform, thereby revealing image unevenness. For that reason, in particular, with respect to a developing roller to be used in an electrophotographic image forming device capable of obtaining a stable color image with high image quality, it has become necessary to more greatly enhance the dimensional accuracy.
As the developing roller to be used in the non-magnetic one-component non-contact development system, for example, there is one principally constructed of a combination of a cylindrical metal base body and a central shaft body as press fitted in both end sections for holding the base body and rotationally driving it. In the developing roller having such a construction, even if only the cylindrical metal base body is finished with a very high accuracy, there may be the case where after press fitting of the central shaft body, a deviation is generated in shaft fitting, etc., whereby the outside diameter deflection may possibly become large. Therefore, press fitting of the central shaft body is also extremely important in obtaining a high-accuracy developing roller. Furthermore, in many cases, after the foregoing shaft body has been press fitted in the both ends of the cylindrical metal base body, the outer surface of the developing roller is subjected to a surface treatment so as to have a required surface roughness by mechanical processing such as sand blast and shot blast, and after further washing, the resulting surface is subjected to a treatment such as nickel plating. On this occasion, when air tightness in the fit section of the central shaft body is poor, a washing liquid, a plating liquid, or the like may possibly invade into the developing roller. When the developing roller having such an invaded liquid therein is put into actual use as it is, since there is some possibility that the invaded liquid leaks out during the use, such a developing roller is an inferior product which should be avoided. Accordingly, the air tightness in the fit section is one of the important functions which are necessary and indispensable for the developing roll having such a construction.
In addition, in order to manufacture a developing roller which has high dimensional accuracy (deflection characteristic), acquisition of tube stock materials having high mechanical rigidity and capable of easily revealing shape accuracy (straightness and coaxiality), a processing method for enabling one to reduce a processing strain (return of residual stress), and the like are needed. Furthermore, in order to frictionally electrify the developer, determination of a roughing surface treatment condition for forming irregularities of the required surface roughness on the outer peripheral surface of the developing roller, determination of a hard plating treatment condition for ensuring friction resistance (maintenance of frictional electrification performance) and corrosion resistance, and the like are important, too.
Here, an invention for making a gap between an electrophotographic photoreceptor and a development sleeve with a shaft uniform in the axial direction by centerless grinding of the shaft and the sleeve cylindrical body at the same time, thereby suppressing the shaft deflection is well known (paragraph 0010 of Patent Document 7).
Furthermore, an invention in which a knurl is formed on the surface of a fit section between a shaft and a cylindrical body to make an interference (press fitting margin) small, whereby a bulge of a sleeve can be reduced and a gap between an electrophotographic photoreceptor and a development sleeve is made uniform is also known (paragraph 0011 of Patent Document 8). In addition, an invention for employing an interference fit relationship for coupling between a shaft and a development sleeve is also known (Patent Documents 9 and 10).
Patent Document 1: JP-B-3-1805
Patent Document 2: JP-A-2003-263019
Patent Document 3: JP-A-7-261438
Patent Document 4: JP-A-2-54287
Patent Document 5: JP-A-2004-109525
Patent Document 6: JP-B-3-35664
Patent Document 7: JP-A-8-74839
Patent Document 8: JP-A-2001-221227
Patent Document 9: JP-A-8-184977
Patent Document 10: JP-A-11-216621